It is well known that both carbon dioxide (CO2) and hydrogen sulfide (H2S) can be removed from gaseous streams by treatment with aqueous amine solutions. Such processes typically comprise absorption of the CO2 and H2S in a column wherein the gas and a lean aqueous amine are countercurrently contacted to produce a rich aqueous amine and a lean gas. At least a portion of the CO2 and H2S is removed from the lean gas, which may be passed to further processing for further CO2 and H2S absorption or the like. Alternatively, sufficient amounts of H2S may have been removed from the treated gas so that it may be safely discharged to the atmosphere or passed to other process uses. In many instances, the CO2 and H2S may be contained in streams comprising hydrogen, carbon monoxide, hydrocarbons and other gaseous components.
The sour gas charged to the amine contacting process may contain CO2 and H2S in varying proportions. When the CO2 content is significant with respect to H2S content (i.e., a CO2:H2S ratio of 3 or higher), then it is found that insufficient H2S may be absorbed for efficient use of the recovered H2S stream in Claus processes for the recovery of sulfur and the like.
The H2S stream is typically recovered by treatment of a rich aqueous amine stream by heating or other treatment as well known to those skilled in the art. Desirably, this H2S stream contains at least 10 and preferably at least 15 volume percent (vol. %) H2S for use as a feedstream to a Claus process.
The operation of amine contacting processes is well known to those skilled in the art. Unfortunately, as the temperature increases in the amine-contacting vessel, the selectivity of the amine absorbent for H2S is decreased. At temperatures above about 150° F., the absorption of CO2 is sufficiently high so that insufficient H2S is absorbed to produce the desired H2S concentration for use in a Claus process. A continuing effort has been directed to the development of a suitably economical and effective process to selectively absorb H2S from gas streams containing CO2 and H2S.
Accordingly, an improved process has been sought whereby H2S may be selectively absorbed from sour gas streams containing H2S and significant quantities of CO2.